Version 2019.02 adds the ability to copy and paste an entire task hierarchy, including all subtasks regardless of how many levels deep in the hierarchy. For example, if you have a complex project with many inter-related tasks that all descend from a root-level task, you can copy that project's root task and paste the entire project as a new task. You can also copy subtasks of one task and paste those into another task.
When a selected task that has subtasks is copied, a message will appear asking if you'd like to also copy the subtasks.
When pasting a copied task while a task is currently selected, a message will appear asking if you'd like to paste as a subtask or a new top-level task.
In this example, the task was pasted as a new top-level task. A different starting date was selected on the Month view prior to pasting. Notice how the entire hierarchy matches what was copied, but with different start and due dates.